Coleman Furnace Ignitor Troubleshooting Guide

The Coleman furnace ignitor is a critical component that starts combustion and keeps a home warm. This guide explains common ignitor problems, testing methods, repair steps, and preventative maintenance to restore reliable operation. It is intended to help homeowners and HVAC technicians quickly diagnose and fix ignitor issues for Coleman furnaces.

Symptom	Likely Cause	Quick Action
No heat, no spark	Failed ignitor or wiring	Inspect ignitor, test resistance, check voltage
Clicking but no ignition	Weak ignitor or flame sensor problem	Test ignitor waveform, clean flame sensor
Ignitor glows but burners won’t light	Gas valve or pressure issue	Verify gas supply and valve operation

How The Coleman Furnace Ignitor Works

The ignitor in most modern Coleman furnaces is an electric hot surface ignitor (HSI) or intermittent pilot spark ignitor. The HSI heats to several hundred degrees and ignites gas at the burners when the control board calls for heat. The ignition sequence is controlled by the furnace control board, which coordinates the inducer motor, pressure switch, gas valve, and ignitor.

Key Components In The Ignition Path:

• Control Board — Sends voltage to the ignitor when safe to fire
• Ignitor Element — Ceramic-based resistor that glows hot
• Pressure Switch and Inducer — Confirm draft before ignition
• Gas Valve — Supplies gas once the ignitor is at proper temperature
• Flame Sensor — Confirms flame; will shut gas off if flame is absent

Common Symptoms And What They Mean

Recognizing symptoms helps isolate whether the ignitor itself is bad or another part of the ignition sequence is failing. Symptoms must be observed during a consistent call for heat to reproduce issues reliably.

No Heat And No Ignitor Glow

This usually indicates a failed ignitor, an open circuit in the wiring, or a control board not sending voltage. First check for error codes on the furnace LED and ensure power and thermostat settings are correct.

Ignitor Glows But Burners Don’t Light

If the ignitor glows but burners do not light, the gas valve or gas supply may be the issue. Confirm the gas supply is on at the meter and inspect the gas valve voltage when the ignitor reaches temperature.

Clicking Sound And Repeated Attempts

Rapid clicking or multiple ignition attempts suggests the furnace is trying to light but failing to sense flame or the ignitor is marginal. The flame sensor or dirty burners can prevent flame establishment despite a functioning ignitor.

Safety First: Tools And Precautions

Before any troubleshooting, turn off power to the furnace at the breaker and shut off gas at the appliance shutoff. Working with electrical and gas systems is hazardous; if uncertain, call a licensed HVAC technician.

Tools Recommended:

• Multimeter with AC/DC and resistance functions
• Clamp meter or voltage meter for live checks
• Screwdrivers and nut drivers for access
• Soft brush and emery cloth for cleaning
• Manufacturer parts list or service manual for model-specific data

Step-By-Step Troubleshooting Procedure

1. Check Basic Power And Thermostat Signals

Confirm furnace has 120V power and the thermostat calls for heat. Verify the furnace display or LEDs indicate a call for heat. If there’s no power, inspect the breaker, blower door switch, and fuses.

2. Observe The Ignition Sequence

Restore power and run a heat cycle. Watch for the inducer motor, pressure switch closing, ignitor glow, and gas valve opening. Note the step where the sequence stops; that reveals where to focus testing.

3. Inspect The Ignitor Visually

Remove the access panel and inspect the ignitor element. Cracks, dark spots, or broken ceramic indicate a failed ignitor. Replace any cracked or visibly damaged ignitors.

4. Test Ignitor Resistance

With power off, disconnect the ignitor leads and measure resistance. Most HSI elements read between 40 and 120 ohms depending on model. Consult the Coleman furnace manual for the exact resistance specification. A reading of infinite or zero indicates failure.

5. Check For Control Board Voltage

With caution and power restored during a heat call, measure the voltage from the control board to the ignitor. HSIs typically receive line voltage (120V). If there is no voltage, suspect the control board or safety interlocks like the pressure switch.

6. Test The Flame Sensor And Gas Valve

After the ignitor glows and gas is supposed to flow, if flame does not occur, check for 24VAC at the gas valve coil during the ignition cycle. If the gas valve receives voltage but gas doesn’t flow, the valve may be stuck or gas supply is interrupted.

Testing Techniques And Expected Values

Using a multimeter correctly narrows down failures. Accurate measurements prevent unnecessary component replacement and speed repair.

• Ignitor Resistance: Typical HSI ranges 40–120 ohms. Refer to the part number spec sheet for exact target.
• Control Board Output: HSIs often receive 120VAC. Spark modules may output high-voltage pulses measured with caution.
• Gas Valve Coil: Usually 24VAC during call for heat. No 24VAC suggests control board or transformer issue.
• Flame Sensor: Should show a small DC microamp signal when flame is present; digital meters may not measure microamps accurately without proper setup.

Common Ignitor Failures And Causes

Ignitor failure usually stems from age, thermal cycling, vibration, or contamination. Frequent short cycles or overheating accelerate wear. Mechanical impact or incorrect handling during service commonly cracks ceramic elements.

• Thermal Shock: Repeated heating and cooling stress the ceramic element.
• Electrical Overvoltage: Surges or incorrect wiring damage the filament.
• Physical Damage: Handling or installation damage causes cracks.
• Contamination: Dust or oil deposits may create hot spots and premature failure.

Replacement Steps For A Coleman Furnace Ignitor

Replacing the ignitor is straightforward when the correct part and model information are used. Use OEM replacement parts to maintain reliability and safety.

Replacement Procedure Overview

1. Turn off power and gas to the furnace.
2. Remove furnace access panels to reach the burners and ignitor.
3. Disconnect ignitor wiring harness carefully to avoid damage.
4. Unfasten mounting screws and gently remove the old ignitor to prevent breakage.
5. Install the new ignitor, secure it, and reconnect the wiring harness.
6. Restore power and run a test cycle to confirm proper operation.

Pro Tip: Handle new ignitors by the ceramic backing or mounting bracket; oils from fingers can shorten element life.

When The Ignitor Tests Good But Furnace Still Fails

If the ignitor measures within spec and glows but the furnace still fails to light, investigate safety switches and air flow components.

• Inspect the pressure switch and inducer for proper operation and clear venting
• Check limit switches that may prevent ignition due to overheating
• Verify adequate gas pressure at the furnace; low inlet pressure prevents ignition
• Ensure the flame rollout switches and door interlocks are not tripped

Maintenance To Prevent Ignitor Problems

Regular maintenance extends ignitor life and reduces ignition failures. Annual professional inspections should include combustion analysis and component checks.

• Clean burners and flame sensor annually to prevent misfires
• Replace air filters regularly to ensure proper airflow and reduce stress on the furnace
• Inspect venting and inducer to maintain correct draft and pressure switch operation
• Schedule annual HVAC tune-ups to catch wear before failure

OEM Parts And When To Call A Technician

Using Coleman OEM ignitors and parts preserves furnace performance and warranty coverage. When the control board, gas valve, or combustion components are suspected, professional service is recommended due to gas and safety risks.

Call A Technician If:

• Ignitor tests normal but furnace still won’t ignite after checking gas supply and safety switches
• Gas valve does not open when 24VAC is present
• There are repeated flame loss or lockout conditions
• Errors on the control board indicate complex failures or component sequencing faults

Troubleshooting Checklist For Quick Diagnosis

Step	Action
1	Confirm power and thermostat call
2	Observe ignition sequence and note where it stops
3	Visually inspect ignitor for cracks
4	Measure ignitor resistance with power off
5	Measure control board output to ignitor during a call
6	Check for 24VAC at the gas valve during ignition
7	Inspect flame sensor and clean if necessary

Frequently Asked Questions

How Long Should A Furnace Ignitor Last?

Hot surface ignitors typically last 3–7 years depending on run time and cycling frequency. Quality of the part and proper maintenance influence lifespan.

Can An Ignitor Be Repaired Instead Of Replaced?

Ignitors are fragile and inexpensive compared to labor; repair is not practical. Replacement with the correct OEM part is the recommended approach.

Is It Safe To Run The Furnace With A Marginal Ignitor?

Running with a failing ignitor can cause prolonged ignition attempts, increased wear, and possible safety lockouts. It is advisable to replace a marginal ignitor promptly.

Resources And Model-Specific Information

Model-specific wiring diagrams and resistance specifications are available in Coleman furnace manuals and on manufacturer websites. Always match the replacement ignitor part number to the furnace model plate for compatibility.

Additional resources include manufacturer technical bulletins, HVAC trade forums, and certified technician training materials for complex diagnostics.

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